The present invention relates generally to electrical connectivity testing more particularly to a method and device for detecting the connectivity of wires, cables, printed circuit board traces and connectors of a device under test during automated test using longitudinal balance measurements.
It is often required to detect the connectivity of an electrical conductor of an electrical device. For example, in an automated test environment in which a run of devices that are identical by design are being tested, electrical continuity testing is standard procedure. Such an automated test environment may test printed circuit boards (PCBs) after manufacture. Connectivity testing is performed in bare-board testing of a printed circuit board (prior to attachment of components and devices) to test the continuity of the traces between pads on the board. Connectivity testing is performed in loaded-board testing (after attachment of some or all the electrical components and devices) to verify that all required electrical connections between the components and the board have been properly completed.
Existing methods to detect the connectivity of electrical conductors such as wires, cables, PCB traces, and connectors in an automated test environment generally require the use of external sensors (e.g., a capacitive measuring probe such as Agilent Technology""s TestJet Probe for the 3070 Automated Tester). External sensors can be ineffective if blocked by a ground plane or if the sensor cannot be physically located near the electrical conductor under test.
An alternative method for detecting the electrical connectivity of electrical conductors in an automated test environment is known as a loopback test. In a loopback test a signal is applied to a pin of the device under test. The signal loops to another pin and is measured using a detector. Loopback testing typically requires the use of custom made loopback cables and requires operator intervention.
Accordingly, a need exists for an alternative method for determining the electrical connectivity of electrical conductors in an automated test environment that does not involve external sensors, loopback cables, or operator intervention.
The present invention is a novel method and apparatus for detecting the connectivity of electrical conductors. In an automated test environment, the connectivity of electrical conductors can be determined without the use of external sensors, loopback cables, or operator intervention.
In accordance with a preferred embodiment of the invention, the measurement apparatus includes a pair of identical valued resistors connected in series between a measurement node and a reference node. A signal generator applies an oscillating signal to an intermediate node between the two series-connected resistors. A measuring device measures the potential between the measurement node and reference node.
In accordance with one embodiment of the invention, a connectivity detection function obtains the following measurements from the meter: the potential Edisconnected when the measurement apparatus is disconnected from the electrical conductor under test, and the potential Econnected when the measurement apparatus is connected to the electrical conductor under test. The connectivity detection function calculates the difference between the potentials Edisconnected and Econnected, and determines that electrical connectivity of the electrical conductor under test exists if the potentials Edisconnected and Econnected are substantially unequal (i.e., outside of a margin of error relative one another). For greater accuracy, the longitudinal balance of the potentials is instead calculated and compared.
In accordance with a second embodiment, a connectivity detection function obtains the following measurements from the meter the potential EKGECxe2x80x94disconnected when the measurement apparatus is disconnected from the known good electrical conductor, EKGECxe2x80x94connected when the measurement apparatus is connected to the known good electrical conductor, the potential EECUTxe2x80x94disconnected when the measurement apparatus is disconnected from the electrical conductor under test, and EECUTxe2x80x94connected when the measurement apparatus is connected to the electrical conductor under test. The connectivity detection function calculates the difference between the potentials EKGECxe2x80x94disconnected and EKGECxe2x80x94connected, and the difference between the potentials EECUTxe2x80x94disconnected and EECUTxe2x80x94connected. The calculated differences are then compared. Electrical connectivity of the electrical conductor under test exists if the differences EKGECxe2x80x94disconnectedxe2x88x92EKGECxe2x80x94connected and EECUTxe2x80x94disconnected xe2x88x92EECUTxe2x80x94connected are substantially equal (i.e., within a margin of error relative one another). For greater accuracy, the longitudinal balance of the potentials and differences are instead calculated and compared. In addition, if the differences EKGECxe2x80x94disconnectedxe2x88x92EKGECxe2x80x94connected and EECUTxe2x80x94disconnectedxe2x88x92EECUTxe2x80x94connected are substantially unequal (i.e., outside of a margin of error relative one another), the values of the measurements may be used to calculate the approximate location of the resistive fault.